Tocainide was administered to 228 patients referred for treatment of recurrent ventricular tachyarrhythmias that were refractory to therapy with conventional antiarrhythmic drugs. After baseline studies, 1200 to 2400 mg tocainide/day was given for 4 days. Tocainide was effective in 49% of 180 patients evaluated with monitoring and exercise testing and in 35% of 48 patients undergoing electrophysiologic testing. No clinical parameter predicted the response to tocainide, although there was a correlation with the effect of lidocaine. Tocainide was selected for long-term treatment in 73 patients who were followed for an average of 26.4 months (range 1 to 92 months). The incidence of sudden death was 4.3% per year and two patients had nonfatal recurrence of arrhythmia. It is concluded that tocainide is effective and well tolerated during long-term use if therapy is evaluated carefully and is individualized.